Key among Ukraine's promised reforms is the independence of the authority in charge of the pipelines from the state-owned energy company Naftogaz, which one Western banker described as a big black box where money just disappears.

President Viktor Yushchenko said Ukraine was determined to root out all kinds of corruption.

Without naming names, the president of the European Commission, Jose Manuel Barroso, asked all political leaders to unite to restore the reliability and transparency of Ukraine's gas transit system.

But Mrs Tymoshenko insisted the network was reliable and told investors that its capacity could be substantially increased for just over $7bn - a fraction, she said, of the price needed for new pipeline projects that would bypass Ukraine.

Later, Russian Energy Minister Sergei Shmatko said the agreement was unilateral and gave it cause for concern.

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